1. Field of the Invention
The present invention relates to a pneumatic booster that is applicable to brake equipments of automobiles, etc.
2. Description of the Related Art
In general, brake equipments of automobiles are provided with a pneumatic booster for enhancement of braking force. In the pneumatic booster, its housing is divided into a constant-pressure chamber (normally kept to negative pressures by depression at engine manifold) and a working-pressure chamber by means of a power piston. Further, a plunger that is connected to the power piton and provided within a valve body is adapted to move by means of an input rod connected to a brake pedal so as to introduce air (positive pressure) into the transformer chamber so as to generate pressure differences between the constant-pressure chamber and the working-pressure chamber. Through the pressure differences, thrust force will be generated onto the power piston. Still further, the thrust force of the power piston affects an output rod through action members so as to operate a master cylinder while counterforce acted from the output rod to the reaction members will be partially fed back to the input rod. Accordingly, pedal control force of drivers can be reduced with large braking force. This also enables control of braking force in a good manner.
In the pneumatic booster for automobiles, for weight saving purposes it is demanded for a thickness of the housing to be thin while maintaining necessary hardness and rigidity thereof. Further, in case that excessive external force is applied to the housing from the side of the master cylinder during vehicle collision, it will be necessary for the housing to be easily deformed in order to repress movement of brake pedals. Accordingly, Japanese Patent Application Laid-Open No. 2000-219126 (hereinafter referred to as Patent Document 1) discloses a pneumatic booster as follows.
In the Patent Document 1, a thick stiffener is mounted on the fore-end portion of a housing by means of a rivet that is adapted to fracture with a certain load. Accordingly, this enables the housing to be easily deformed in case that excessive external force is applied to the housing, whereby traveling amount of a brake pedal can be minimized.
However, in the Patent Document 1, it would be necessary to have the stiffener and the particular rivet thereby increasing a number of parts while reducing production efficiencies.